MASS- ACTION OF BACTERIA. 



cell-division; (2) the destructive action of antiseptic plant-substances, e. g., acids, before 

 these can be neutralized or otherwise destroyed by the substances produced by the mul- 

 tiplying bacteria. 



In some instances, the introduction of a very considerable mass of bacteria seems to 

 be necessary to induce disease ; in other cases a very few are sufficient. It would be extremely 

 interesting to know the minimum number capable in any given case of inducing disease. 

 This could be determined easily by the dilution method, and still more readily and with 



Fig. 21.* 



Fig. 22 t 



absolute accuracy by the use of Barber's apparatus, but no one seems to have made any 

 exact experiments. Good organisms for experimental purposes would be Bacillus phytoph- 

 thorus, Bacillus tracheiphilus, Bacillus amylovorus, and Bacterium campestre, care being 

 taken, of course, to select sensitive varieties and susceptible tissues, and to have all other 

 factors comparable. 



SECONDARY TUMORS AND METASTASIS. 



Secondary foci of overgrowth occur in the olive and in the daisy as the result of internal 

 infection. The writer has obtained them frequently in both plants by pure culture inocula- 

 tions (plates 6 and 7, and fig. 23). The organisms pass through the tissues of the stems or 

 leaves and set up irritations which lead to hyperplasias in particular spots in the deeper tis- 

 sues. These tissue enlargements, later on, break through to the surface. Sometimes these 

 secondary growths arise at a considerable distance from the primary tubercle. In case of 

 olives inoculated in 1910 the writer observed numerous deep tubercles develop at a distance 

 of i, 2, and 3 feet from the point of inoculation within a period of 7 months in actively 

 growing plants, both down and up the shoot. The movement is more apt to be up the stem 

 or leaf, i. e., with the transpiration current, than down the stem. 



In the olive a distinct channel of infection is traceable from the primary to the sec- 

 ondary tubercle. This is usually (so far as observed) a narrow pathway in some part of the 

 inner wood, the tissues being more or less stained and disorganized, and the bacteria present 

 in abundance and easily demonstrable without staining. Whether similar downward 



*FiG. 21. Three figures from Peirce's paper: 



(1) Two root-hairs of Bur clover infected by nodule bacteria, showing characteristic bending at point 

 of infection, x 50. 



(2) The lower of two root-hairs in i, showing mass of bacteria in concavity of coil and infection thread 

 running from this point through the hair, x 300. 



(3) Another infected and coiled root-hair, infection thread growing close to nucleus of hair, x 300. 



fFiG. 22. Two figures from Peirce's paper on Root Tubercles of Bur Clover: 



(10) Section of a tubercle near meristem. Direction in which meristem lies is indicated by arrow. Section 

 stained by Fleming's triple stain and differentiated, after anilin gentian violet, by Gram's iodine. Course of 

 infection threads is definitely toward tubercle-meristem and generally toward nucleus of cell entered, x 200. 



(n) One cell from 10, showing' solid infection strand (zoogloeae) in which separate bacteria can be dis- 

 tinguished, x 1000. 



